The present invention relates to a tire condition monitoring system for providing tire operation parameter information, such as tire inflation pressure, to a vehicle operator. The present invention relates specifically to a tire condition monitoring system that utilizes a reception arrangement and process to eliminate lost data from a tire-mounted sensor unit during vehicle operation.
Numerous tire condition monitoring systems have been developed in order to provide tire operation parameter information to a vehicle operator. One example type of a tire condition monitoring system is a tire pressure monitoring system that detects when inflation pressure within a tire drops below a predetermined threshold value.
There is an increasing need for the use of tire pressure monitoring systems due to the increasing use of xe2x80x9crun-flatxe2x80x9d tires for vehicles such as automobiles. A run-flat tire enables a vehicle to travel an extended distance after significant loss of air pressure within that tire. However, a vehicle operator may have difficulty recognizing the significant loss of air pressure within the tire because the loss of air pressure may cause little change in vehicle handling and little change in the visual appearance of the tire.
Typically, a tire pressure monitoring system includes a pressure sensing device, such as a pressure switch, in a unit at each tire and a communications link for conveyance of tire pressure information from the location of each tire to a central receiver unit. The central receiver unit is typically connected to an indicator (e.g., a display) located on a vehicle (e.g., on an instrument panel).
The communications link between each tire-based unit and the central receiver unit is often a wireless link. In particular, radio frequency signals are utilized to transmit information from each of the tire-based units to the central receiver unit.
Typically, tire condition monitoring systems have the ability to provide current tire condition information to a vehicle operator while the vehicle is in operation. For the systems that include tire-based units that are located within a pressurized cavity of a wheel/tire assembly, operation of the tire condition monitoring system entails operation of the tire-based units during rotation of the associated vehicle tires.
Turning to the radio frequency signals that are transmitted from the tire-based units to the central receiver unit, the signals typically comprise a series (e.g., a pulse string) of data bits. The time necessary to completely transmit a pulse string depends upon the number of bits to be transmitted, the type of transmission format (e.g., amplitude, shift key, or pulse-width modulation), carrier frequency, receiver sensitivity, etc. Typically, signal data rate is not very high. Commonly, the signal data rate is at a rate of a few kilohertz.
A typical transmission time for a message that has 54 bits would be about 18 milliseconds at a data rate of 3 kHz. For a vehicle that has 14-inch radius tires and that is traveling at relatively high rate of speed (e.g., 380 kilometers/hr.) each tire turns approximately 49 times/second. In other words, each turn of a tire takes 20 milliseconds. Thus, it can be easily seen that approximately one full rotation of a tire occurs during the complete transmission of the 18 milliseconds data string.
As a tire rotates, a direct path between a tire-based unit and a vehicle-based unit changes. As the direct path changes, the objects that are located along the direct path change. In one scenario, it is possible that a bulk of the associated metal wheel, suspension components, etc. is alternately in and out of the direct path. In general, the movement of the tire-based unit relative to the associated wheel and other components during tire rotation causes the transmitted signal to be subject to variation in polarization, multi-pass interference, fading, etc. These influences cause variation in the strength of the signal at the vehicle-based receiver.
Other factors can affect signal strength. For example, change in the environment surrounding the vehicle will cause variation in signal strength. One example of an environment change is a car or object that passes relatively near to the vehicle. In sum, it is possible that signal strength at the central receiver unit may become so weak during a portion of a pulse string that the central receiver is not able to receive that portion of the pulse string. Accordingly, the message is lost.
In accordance with one aspect, the present invention provides a tire condition communication system for a vehicle. Sensor means, associated with a tire, sense at least one tire condition. Transmitter means, associated with the tire and operatively connected to the sensor means, transmits a signal that has a data rate and that indicates the sensed tire condition. Receiver means, associated with the vehicle, receives the signal. The receiver means includes a plurality of antennas, each for receiving the transmitted signal, and means for switching among the plurality of antennas at a rate that is quicker than the data rate of the transmitted signal.
In accordance with another aspect, the present invention provides a tire condition communication system for a vehicle. A tire condition sensor and a transmitter unit is associated with a tire. A transmitted signal from the unit has a data rate and indicates a sensed tire condition. A receiver unit is associated with the vehicle. The receiver unit includes a plurality of transmitted signal receiving antennas. The receiver unit includes a plurality of switches, with each switch being interposed between a respective one of said antennas and another portion of the receiver unit. The receiver unit including a switch-controlling controller that controls the switches to sequentially connect one antenna at a time to the other portion of the receiver at a rate that is quicker than the data rate of the transmitted signal.
In accordance with another aspect, the present invention provides a tire condition communication method for a vehicle. At least one tire condition is sensed at a tire. A signal that indicates the sensed tire condition is transmitted from the tire. The transmitted signal has a data rate. The signal is received for use in determining the indication of the sensed tire condition. Switching among a plurality of antennas at a rate that is quicker than the data rate of the transmitted signal is utilized to receive the signal for use in determining the indication of the sensed tire condition.